Frequency control apparatus



April 24, 1956 H. E. RENFRO 2,743,390

FREQUENCY CONTROL APPARATUS Filed June 4, 1951 IN VEN TOR. Harold ERen'fro United States Patent O 2,743,390 FREQUENCY CONTROL APPARATUSHarold E. Renfro, Seattle, Wash. Application June 4, 1951, Serial No.229,855

14 Claims. (Cl. SIS-14) plate will cause a plate output of selectedfrequency.

A further object of the invention is the provision of an electron tubewherein two sets of concentric grids, each having a polyphasealternating voltage applied thereto, are located between the cathode andanode, whereby the inner set of grids convert the emitted electrons intoa rotating beam which may make one or less revolutions for each cycle ofthe applied grid voltage. The voltage applied to the outer set of gridsis in a predetermined direction so that the output of the anode is equalto the sum of the grid frequencies if the direction of the said voltagesand rotation of the beam are opposite, or equal to the difference of thegrid frequencies if these two movements are in the same direction.

Another object of the disclosed invention is the incorporation into thesystem of a control for the abovementioned electron tube consisting of anew method of obtaining a distortionless four phase alternating voltagefrom single phase voltage such as produced by amicrophone.

One important advantage of the invention lies .in the fact that with anelectronic application of the device it is possible to furnish singlesideband suppressed carrier amplitude modulated signals for radio andcarrier communication.

Still other objects and advantages will become apparent from thefollowing description of the present invention illustrated in theaccompanying drawing, in which:

Figure 1 is a schematic view showing a mechanical application of theinvention.

Figure 2 is a schematic view of a portion of the mechanical applicationshown in Figure 1 taken at right angles to Figure 1. v

Figure 3 is a schematic view of a modification of the mechanicalapplication shown in Figure 1.

Figure 4 is a schematic view of an electronic application of theinvention.

Figure 5 is a diagrammatic view of a circuit with an input resistancehigh in comparison to the reactance. 'The output voltage is drawn fromacross the reactance.

Figure 6 is a diagrammatic view of a circuit with an input reactancehigh in comparison to the'resista'nce. The output voltage is drawn fromacross the resistance.

Figure 7 is a diagrammatic view combining the circuit of Figures 5 and 6with a current transformer replacing the resistor in Figure 6. i

As previously mentioned, my system is applicable to either mechanical orelectrical input frequencies. Although the entire principle is-relatively simple, it is believed that an explanation of the mechanicaladaptation first would be more in keeping with a logical and cleardisclosure of the invention.

The basic conception of the idea is shown schematically in Figure 1 ofthe drawing. A conventional light source 10 and a photocell 11 arespaced from one another, as shown. A plate 12 is positioned betweenlight source 10 and photocell 11 and is provided with an elongated slit13 in order to concentrate the light passing from the source to thephotocell into a defined beam designated generally as 14. The lightsource, plate and photocell are mounted rigidly together so to bemovable as a unit, the purpose of which will become apparent as thedescription progresses.

A long strip of copper which may be approximately ii: Of an inch wideand of an inch thick is twisted to form a screw-like element with apitch of about two inches. This screw is placed between plate 13 and thephotocell in the path of light beam 14 and forms an opaque shutter 15adapted to rotate about its longitudinal axis as shown by the arcuatearrow in Figure 1. This rotation may be in either a clockwise orcounterclockwise direction. It will be seen from Figures 1 and 2 thatthe beam of light has its narrow dimension parallel to the axis ofshutter 15 and its width is substantially equal to the maximum width ofthe shutter, i. e. of an inch. The amount of the light beam whichimpinges on the photocell 11 will thus vary in accordance with itsinterruption by the projection of revolving shutter 15. The lightassembly comprising the source, plate, and photocell can move parallelto the axis of the shutter in either direction as shown by the verticalarrow in Figure 1.

'In the operation of this setup, conventional electrical circuits arecompleted to show any variation of light intensity on photocell 11.Thus, when the screw member 15 is continuously rotated at a constantspeed, the portion of member 15 that is in the light beam will act as ashutter, diminishing the light :received by the photocell when the flatside, or greatest width, of the shutter is presented to the beam andincreasing the light received when the narrow edge is presented to thebeam. This progressive increase and decrease of light passed by therotating shutter is clearly illustrated in Figure 2 of the drawing. Theminimum intensity'is apparent when the greatest width of the shutter isperpendicular to the path of the light beam as shown at 15a in Figure 2,and the intensity increases as the involved portion of the shutterapproaches alignment with the light ray until the position shown as 15bis reached, at which time a maximum portion of the light ray is allowedto pass to the photocell. Thus, one cycle of output energy will bedelivered by the photocell for each half revolution of shutter 15. It ispointed out that proper shaping of the screw-like shutter will produce asine wave output if desired.

The frequency of the described energy output has up to this point beendependent only on the speed of rotation or frequency of shutter 15. Whenthe shutter '15 is considered as a screw, an imaginary nut placedthereon would move along the axis of the shutter in one direction at alinear speed of two inches per revolution when using the previouslymentioned arbitrary screw pitch as an example. If the light assembly ismoved in this direction at 'the same linear speed as the nut, there willbe no variation of intensity brought about by the shutter and the outputfrequency of the photocell 11 be comes zero. By the same reasoning it isapparent that if the light assembly is moved in the same direction athalf the imaginary nut velocity, the output frequency is half theoriginal frequency as obtained with a stationary assembly.

It can be concluded from the above explanation that 'lar path. aperturedplate 18 rotate about the same axis as the' .ence in speeds.

when the light assembly is moved in the same direction as the imaginarynut, the output frequency is proportional to the difference between thelinear velocity of the light assembly and the angular velocity of theshutter.

- On the other hand, if the light aessembly is moved at the imaginarynut velocity, but in the opposite direction, the output frequency of thephotocell becomes twice that at light assembly standstill. Likewise, athalf nut velocity the out-put frequency is one and one-half-t-imestheoriginal frequency. Thus when the light assembly is moved in adirection opposite to that of the imaginary nut, the

output frequency is proportional to the sum of the linear velocity ofthe light assembly and the angular velocity of the shutter. It is'to benoted that this sum frequency is caused by reversal of one directionalmovement only.

The modification shown in Figures 1 and 2 are ideal for illustration ofthe principle involved but its actual use is impractical due to the factthat the device is limited by the length of shutter 15. 'In order 'toovercome this difliculty a modified form of the device can beconstructed with practicability and is schematically shown in Figure 3of the drawing.

If the ends of the shutter were to be joined, it would make a closedring 16 that could be rotated either about a central axis as shown inFigure 3 or about its own axis which now becomes a circle. Only rotationabout the center of the circle will be discussed here although eithermethod is useable. With this construction, the effective length of theshutter is infinite sinceit rotates in a circu-' In this modificationthe light source 17 and shutter ring, the elongated slit 19 hearing thesame directional relationship with the dimensions of the screw shutteras in the first modification in Figures 1 and 2.

The above elements are surrounded by a cylinder designated generally as20 and which has a light sensitive inner surface 21 which acts as aphotocell. With shutter 16 removed, the light beam 22 can rotate at anyspeed without producing any variation in output of the photocell surface21. Beam intensity and photocell sensitivity are both uniform. Insertionof the shutter, held stationary, causes the beam intensity and photocelloutput to vary, producing one cycle of photocell output energy for each180 degree twist of the shutter.

Rotation of the shutter about the central axis in a direction oppositeto light beam rotation produces an increase in the frequency of thephotocell output that is exactly proportional to the sum of the twospeeds.

Rotation of the shutter about the central axis in the same direction aslight beam rotation but at a lower speed produces an output frequencyexactly equal tothe differ- When these two relative speeds are equal theoutput frequency becomes zero. Shutter speeds greater than beam speedsin the same direction have definite uses such as in demodulation butwill not be discussed here in the interest of simplicity of description,

A still further use of the principle involved in this in vention is itsapplication to an electronic device. The previously mentioned lightsource and 'phototube (Fig-- ure 3) are replaced by a source ofelectrons and acoucentric collecting plate as shown in Figure 4. Thesource of electrons is in the form of a small diameter filament 23heated electrically providing a cathode for' the electron tube. This maybe considered a line source of electrons without serious error.Surrounding the electron emitting filament are four separate plane grids24a, 24b, 24c and 24d. The segments are'about equal in length to thelength of the filament and when combined form a square enclosure withthe filament in the center asshown in Figure 4.

If a set of four-phase sinusoidal voltages, 90 degrees apart in timephase, is applied between the cathode and the four grids in such amanner that the time-phase rotation of the voltages is in the same orderas the spacephase relationship of the four grids taken either clocka besupplied with four-phase sinusoidal voltage with rewiseorcounter-clocltwise, a rotating electric field is pro- 7 duced whichhasa speed of rotation equal to the frequency of the applied voltages.The field can readily be made uniform if the four grids are biasednegatively with respect to the cathode so that no grid current flowsandthe light source and associated slit in the mechanical ap-' plication ofthe invention. The four-phase voltages required may be easily derivedfrom a set of two-phase voltages 90 degrees apart'in time phase byproper electrical connections.

The cylindrical plate 25 forms the anode for the electron tube" and isconcentric with the filament and grids. The plate being made positivewith respect to the filament, collects the electrons passed by the gridsegments 24a, 24b, 24c, and 24d. Obviously, with the input remainingconstant, there is no variation in intensity of the electron beam andthe plate current remains constant as the electron beam rotates. Theoperation up to this point is the equivalent of the mechanicaladaptation of the invention with the screw-like shutter removed.

A second set of four plane grid segments 26a, 26b, 26c

and 2641, are located between the previously mentioned grid segments andthe plate 25. One set of grids may be oriented on the central axis inany manner that will give the proper fieldnot necessarily as drawn.These may spect to the cathode at a frequency lower than that'applied tothe inner grid segments (24a, 24b, 24c and 24d). A sine wave output maybe obtained by optimum voltage adjustment of the outer grid segments.Thus it will be seen that with a constant amplitude, frequency andvoltage applied to the outer grid, the plate output frequency will beequal to the diiference'in frequency of the inner and outer grids whenthe rotation of their two fields is in the same. direction. Likewise,the plate output frequency is equal to the sum of the frequencies if thetwo fields rotate in opposite directions; j Considering modulation ofthe output in either the mechanical .or electronic application of the'invention, it is pointed out that if thewidth of the shutter in thefirst instance could belessened while'in operation, the light impingingon the photocell would not be completely cut off each half revolution.Since the output the photocell varies directly with the change of lightintensity, a small variation in intensity will give a small alternatingcurrent output, while a large variation will give a large output as longas zero light'intensity is never reached. This amplitude modulates theoutput, which is at the sum or difference frequency.

In regard tothe electronic adaptation of the invention,

the four-phase potential on the outer grid (segments 26a,

' tained. ,The sum or difference-frequency output of the plate ismodulated in a manner similar .to the paragraph above. Either intensityvariation or area variation of the beam or a combination of the two maybeused for modulation. Exponential or other special purpose grids maybeused if'n'on-linear output is desired.

Having descr'bed my novelly constructed electron tube,

1 wishto point out that one obvious electronic applicav tion of thedevice is to furnish'single sideband suppressed carrier amplitudemodulated signals for radio and carrier communication. If the innergrids are driven by the base radio frequency and four-phase modulation(such as voice or music) is applied to the outer grids, the plate outputis only the upper or lower sideband as selectedby relative phaserotations previously explained. Since the opposite sideband is notproduced, the customary filters to suppress it are unnecessary. The basefrequency is not present in the output. Of course, a screen grid may beadded between the outer grid and the plate, or other methods may be usedto make the plate current independent of plate voltage. Demodulation mayalso be accomplished with a similar tube structure.

It is well known that electrical currents produced by sound wavesimpinging on a microphone are normally single phase and'of manyfrequencies. In order to control the electron tube described herein,this single phase input must be changed to polyphase. I have met thisproblem by incorporating in my system a new method of obtainingdistortionless four-phase from single phase, such as produced by amicrophone. From this fourphase output, any desired number of phases maybe obtained.

Referring first to the circuit 27 in Figure 5 of the drawing, consider acapacitive reactance in series with a resistor 28. Initially there is novoltage across the condenser Z9 and no current flowing in theconductors. When a single phase sine wave voltage is impressed on theterminals, the voltage across the condenser lags 90 degrees behind theapplied voltage, if the capacitive reactance is low compared to theresistance.

Consider the equation where Q is the condenser charge, C is thecapacitance and E is the maximum value of A. C. voltage. If the voltagebuilt up on the condenser is too low to affect the flow of currentthrough the resistor, the voltage on the condenser is maximum at the endof the first alternation, 180 degrees, then decreases to zero at 270degrees and changes in reverse polarity, thus giving the required 90degrees lag. Q is proportional to the product of current and time, sothat a constant current for a shorter time gives a lower impressedvoltage on the condenser. This means that there is a straight line dropin condenser voltage as the frequency is increased. The above may beconsidered a constant current circuit, i. e., the output no load voltageis proportional to input current and inversely proportional to inputfrequency.

A constant A. C. voltage input applied to circuit 30 is diagrammaticallyshown in Figure 6 of the drawing. A high reactance in this case limitsthe current, which is indicated by the voltage across the very lowresistance (31) which is too small to affect the voltage distribution.The input current and consequently the output voltage across resistor 31leads the input voltage by 90 degrees, if the input is supplied from asource of low impedance compared to the capacitive reactance shown.

The frequency response is directly proportional. That is, an increase infrequency produces an increased output voltage. Since Q=CE and E=IZ thenZ, the A. C. impedance, decreases as the frequency rises; so for aconstant B, the current I must increase giving a linear output voltageincrease across resistor 31 with increased frequency.

Figure 7 shows a circuit 32 which is a combination of the circuits shownin Figures 5 and 6 with a transformer 33 replacing the resistor 31 ofthe constant voltage circuit in Figure 6. The replacement of theresistor by a current transformer produces beneficial results, in thatphase reversal may be accomplished so that the output voltages of thecircuits in Figures 5 and 6 will add in phase. The sum of the outputscan be made independent of the input frequency when both inputs aresupplied from the same single phase power source. The output is 90degrees out of phase with the input, and the output voltage can be madeequal to input voltage.

At low frequencies, the lower circuit (27) in Figure 7,

supplies most of the output voltage. At some medium frequency, eachcircuit supplies half the voltage. At high frequencies, the uppercircuit (30) supplies most of the output voltage. This gives adistortionless degrees phase change that, when used with the inputvoltage, becomes a four-phase supply.

The upper input circuit (30) can well be supplied with input voltagefrom a loaded power output triode which will give good voltageregulation. The other input circuit (27) can be supplied by a pentodeoperated on the constant current portion of its curve and this will takethe place of the series resistor shown. Triode and pentode control gridsmay be driven by the same input voltage.

The circuit shown in Figure 7 will drive the outer grid segments 26a and26c while grids 26b and 26d are driven by the original input frequencyto produce a single sideband suppressed carrier modulated output withthe electron tube herein described.

From the foregoing description of the present invention it will be seenthat I have provided a method of controlling output frequency which canbe utilized, among other things, to improve radio and carriercommunication by furnishing single sideband signals or to convert asingle sideband signal back to audio.

in some cases only the sum or difference frequency is required andmodulation is unnecessary.

The functions of grids 24a, 24b, 24c and 24d may be combined with thoseof 26a, 26b, 26c and 24d so a single grid structure and appropriatecircuits can deliver the sum or difference of the inputs.

While a preferred form of the invention has been shown and described, itwill be understood that variation in details of form may be made withoutdeparture from the invention as defined in the appended claims. Thiscircuit may be used with other tubes and this tube may be used withother appropriate circuits.

I claim:

1. An apparatus for controlling electrical output frequency comprising acentral source of emission of energy, a concentric energy receivingelement surrounding and spaced from said source, means connected to saidsource of energy for converting the emitted energy into one or morerotating beams varying according to a continuous wave shape and having aselected angular velocity and direction, means independent of saidconverting means, located between said converting means and said elementfor varying the intensity of said beams with one or more selectedfrequencies moving in a given direction whereby the frequency of theelectrical output of the energy receiving element is controlled by thevelocity and direction of the beam relative to that of said movingfrequency.

2. An apparatus for controlling electrical output frequency andamplitude comprising a central source of emission of energy, aconcentric energy receiving element surrounding and spaced from saidsource, means connected to said source of energy for converting theemitted energy into one or more rotating beams varying according to acontinuous wave shape and having a selected angular velocity, meansindependent of said converting means, located between said convertingmeans and said element for varying the intensity of said beam with aselected frequency moving in the same direction as the rotating beamwhereby the frequency of the electrical output of the energy receivingelement is equal to the difference between the velocity of the rotatingbeam and that of said moving frequency.

3. An apparatus for controlling electrical output frequency comprising acentral source of emission of energy, a concentric energy receivingelement surrounding and spaced from said source, means connected to saidsource of energy for converting the emitted energy into one or morerotating beams varying according to a continuous wave shape and having aselected angular velocity, means independent of said converting means,lo-

cated between said converting meansand said element 7 for varying theintensity of said beams with a selected frequency moving in a.,directionopposite to that of the rotating beams whereby the frequency of theelectrical output of the energy receiving element is equal to the sum ofthe velocity of therotating beam and that of said moving frequency.

viding a polyphase alternating voltage applied thereto to produce one'or more rotating beams of; electrons varying according to a continuouswave shape and directed toward said anode, a second grid structuresurrounding the cathode and located between the first mentioned gridstructureand the anode; means independent of said beam-rotating means,providing a polyphase alternating voltage to said second grid structurein a given direction whereby the frequency of the output of the anode iscontrolled by the relative input frequencies and directions'of thegrids. V V V 5. An apparatus for controlling electrical output frequencycomprising a cathode and a single anode surrounding it, beam-rotatingmeans comprising a multiple grid structure'concentric with said anodeand means connected between the cathode and said grid structure,providing a polyphase alternating current applied thereto to produce oneor more rotating beams of electrons varying according to a continuouswave shape and di rected toward said anode, a second grid structuresurrounding the cathode and located between the first mentioned gridstructure and the anode; means independent of said beam-rotating means,providing a polyphase alternating current to said second grid structurein the same direction as the rotating beam whereby the frequency of theoutput of the anode is'equal to the difference between the inputfrequencies of the grids.

6. An apparatus for controlling electrical output frequency comprising acathode and a single anode surrounding it, beam-rotating meanscomprising a multiple grid structure concentric with said cathode andmeans connected between the cathode and said grid structure, providing apolyphase alternating voltage applied thereto .to produce one or morerotating beams of electrons vary ing according to a continuous waveshape and directed toward said anode, a second grid structuresurrounding the cathode and located between the first mentioned gridstructure and the anode; means independent of said beamrotating means,providing a polyphase alternating voltage to said second grid structurein a direction opposite-to the directional movement of the rotating beamwhereby the output frequency of the anode is equal to the sum of theinput frequencies of the grids, V

7. An apparatus for controlling electrical output frequencycomprising acathode and a single anode 'surrounding it, beam-rotating meanscomprising a multiple grid structure surrounding said cathode and meansconnected between the cathode and said grid structure, providing apolyphase alternating voltage applied thereto to produce one or morerotating beams of electrons varying according to a continuous waveshape'and directed toward said anode, a second grid structuresurrounding the cathode and located between the first mentioned gridstructure and the anode; means independent of said beam-rotating means,providing a polyphase alternating current to said second grid structurein a given direction whereby the frequency and amplitude of the outputof the anode circuit is controlled by the relative input frequencies ofthe grids, and means connected to. the grids for changing single phasevoltage todistortionless poly- I phase voltage for driving said grids.

8. An apparatus for controlling'electrical output fre- H comprisinga-centralsou'rce of emission of energy; a single, continuousenergy-receiving element surrounding quency and amplitude comprising acathode and'a single 'anode concentric therewith, beam-rotating meanscomprising a multiple grid structure surrounding said cathode and meansconnected between the cathode and said grid j structure, providing apolyphase alternating voltage applied thereto to produce one or morerotating beams of electrons directed toward said anode, a second gridstructure surrounding' the cathode and located between the firstmentioned grid structure and the anode; means independent of saidbeam-rotating means, providing a polyphase alternating voltage to saidsecond grid structure in a given direction whereby 'the frequency andamplitude of, the output of the anodecircuit is controlled by therelativeinput frequencies and amplitudes of the grids means connected tothe grids for changing single phase current to distortionless polyphasecurrent for driving said grids, and meanscomprising a circuit which addstwo voltages, one of which is taken across 'a' reactor approaching zero.reactance'compared to circuit resistance and the other voltage which isproduced by the current through a reactor having a reactance approachinginfinity as compared to the supply circuit resistance,

single phase source. V 9. The method of controlling electrical outputfrequency and amplitude of a circuit having a single ano de consistinginconverting within said anode a field of electrons into a rotating beamof electrons varying according to a continuous wave shape and,intercepting said beam with a moving electrical field so as to vary theintensity of theelectrons impinging theranode. V V

10, The method of controlling electrical output frequencyand amplitudeof a circuit having a singleanode consisting in imposing within saidanode a polyphase al ternating current or voltage on a field ofelectrons -to produce one or more rotating beams, of electrons varyingaccording to a'continuous wave shapeand, intercepting said beams with apolyphase alternating current orivoltage moving in the same direction asthe beam so as to vary the intensity of the electrons impinging theanode where- 'by the output frequency of the anode circuit will equalthe ditference of the two input frequencies.

11. The method of controlling electrical output'frequency and amplitudeof a circuit having a single anode consisting in imposing within saidanode a polyphase alternating current or voltage on a field of electronsto produce one or more rotating beams of electrons varying I quency andamplitude comprising the steps of producing a beam of energy emanatingfrom a centralpoint to .a single anode, within said anode rotating thebeam around said central point, and causing said beam to varyaccording'to a continuous wave shape, intercepting said beam with amoving frequency so as to vary the beam intensity, and receiving thebeam on said anode concentric with said central point, so that theoutput frequency is afunction of both the frequency of,rotation of thebeam and the interrupting frequency. t r V V 13. Apparatus for providinga modulated output wave,

and spaced from said source; a plurality of perforate members interposedbetween said source of emission and said energy receiving element; meansincluding said per-c V forate members for converting the emitted energyfrom said' source into a rotating. pattern varying according/to acontinuous wave shape and passing simultaneously through said perforatemembers to the said element;'and

both of the above voltages originating from the same means locatedbetween the said perforate members and said energy receiving element,for controllably varying the intensity of said pattern, thereby tomodulate the output of energy to the said element.

14. Apparatus for controlling electrical output frequency comprising acathode for emitting electrons and a single anode surrounding thecathode; means for rotating the emission from said cathode, comprising amultiple grid structure surrounding the cathode and circuit meansconnected between the cathode and said grid structure, applying apolyphase alternating voltage thereto to produce a rotating pattern ofelectrons varying according to a continuous wave shape and directedtoward said anode and passing simultaneously through said multiple gridstructure; a second grid structure surrounding the cathode and locatedbetween the first-mentioned grid structure and the anode; meansindependent of said emission rotating means, appyinga polyphasealternating voltage to said second grid structure in a given direction10 whereby the frequency of the output of the anode is controlled by therelative input frequencies and directions of the grids.

References Cited in the file of this patent UNITED STATES PATENTS2,185,684 Bennett Jan. 2, 1940 2,248,239 Jarvis July 8, 1941 2,345,115Hall Mar. 28, 1944 2,363,791 Holden Nov. 28, 1944 2,390,884 Jansky Dec.11, 1945 2,396,211 Skellett Mar. 5, 1946 2,461,250 Bailey Feb. 8, 19492,476,349 Beard July 19, 1949 2,500,574 Rudenberg Mar. 14, 19502,533,401 Schramm Dec. 12, 1950 FOREIGN PATENTS 328,680 Great BritainMay 5, 1930

